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Establish the presence and composition of TRAPPIST-1 c’s atmosphere

Ascertain whether TRAPPIST-1 c possesses an atmosphere and, if present, characterize its dominant composition (e.g., O2, H2O, CO2) consistent with JWST/MIRI thermal phase-curve measurements and 15 μm eclipse constraints.

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Background

The ZH analysis modeled the combined phase curve with sinusoidal and quasi-Lambertian forms and retrieved dayside and nightside fluxes and phase offsets for TRAPPIST-1 c. Due to the relatively small contribution of TRAPPIST-1 c’s signal and broad uncertainties, the analysis could not decisively determine atmospheric presence or composition.

Although previous eclipse measurements allow some scenarios, the phase-curve retrieval alone leaves the atmospheric status and composition of TRAPPIST-1 c unresolved, with thin, greenhouse-poor atmospheres remaining plausible.

References

This leaves the existence of an atmosphere and the atmospheric composition of TRAPPIST-1 c still unclear based on the double phase curve retrieval but combined with previous eclipse depth of TRAPPIST-1 c, a thin atmosphere is favored (see atmospheric modeling below).

— First JWST thermal phase curves of temperate terrestrial exoplanets reveal no thick atmosphere around TRAPPIST-1 b and c (2509.02128 - Gillon et al., 2 Sep 2025) in Methods, Data reduction and analysis (ZH), Data Analysis (Stage 4–5)